1. Field of the Invention
The present invention relates to an actinic-ray- or radiation-sensitive resin composition, an actinic-ray- or radiation-sensitive film therefrom and a method of forming a pattern. More particularly, the present invention relates to an actinic-ray- or radiation-sensitive resin composition that is suitable for use in an ultramicrolithography process applicable to a process for manufacturing a super-LSI or a high-capacity microchip, a process for manufacturing a nanoimprint mold, a process for producing a high-density information recording medium, etc., and other photofabrication processes, and relates to an actinic-ray- or radiation-sensitive film from the composition and a method of forming a pattern. Further more particularly, the present invention relates to an actinic-ray- or radiation-sensitive resin composition, actinic-ray- or radiation-sensitive film therefrom and method of forming a pattern that can find appropriate application in the microfabrication of semiconductor devices by electron beams, X-rays or EUV light.
2. Description of the Related Art
In the microfabrication using a resist composition, the formation of an ultrafine pattern is increasingly required in accordance with the realization of high integration for integrated circuits. In accordance with this requirement, the trend of exposure wavelength toward a short wavelength is seen. For example, the development of lithography technology using electron beams, X-rays or EUV light in place of an excimer laser light is progressing (see, for example, patent reference 1).
In the lithography using electron beams (EB), it is known that the influence of electron scattering, namely, forward scattering in a resist film is lessened by increasing the acceleration voltage of EB. Therefore, in recent years, the acceleration voltage of EB tends to be increased. However, increasing the acceleration voltage of EB, although lessening the influence of forward scattering, increases the influence of the scattering of electrons reflected by a resist substrate, namely, backward scattering. When it is intended to form an isolated line pattern of large exposure area, this influence of backward scattering is especially grave. Accordingly, for example, an increase of the acceleration voltage of EB might lead to the possibility of a deterioration of the resolution of the isolated line pattern.
In particular in the patterning of a photomask blank for use in semiconductor exposure, as a light shielding film containing a heavy atom, such as chromium, molybdenum or tantalum, is present in a layer under a resist film, the influence of backward scattering attributed to a reflection from the resist underlayer is more conspicuous than in the application of a resist onto a silicon wafer. Therefore, when an isolated line pattern is formed on a photomask blank, the influence of backward scattering is so grave that the possibility of resolution deterioration is high.
A chemically amplified positive resist is generally a photosensitive composition comprising a compound (photoacid generator) that when exposed to light, generates a strong acid and a compound in which a hydrophobic acid-unstable group is decomposed by the catalytic action of generated acid to thereby convert the compound to an alkali-soluble substance. The photosensitive composition may further comprise a basic compound in order to inhibit any dark reaction in unexposed areas. The presence of a basic compound makes it possible to deactivate through a neutralizing reaction any acid generated due to the influence of scattered electrons to thereby suppress any film thinning in unexposed areas. However, when an acetal group exhibiting a low activation energy in acidolysis reaction is used as an acid-unstable group, the decomposition reaction of the acid-unstable group competes with the neutralizing reaction between generated acid and basic compound, so that the film thinning in unexposed areas cannot be completely suppressed. In particular, the resolution of an isolated line pattern is deteriorated.
As a method for enhancing the resolution of an isolated line pattern, the use of a resin containing a group capable of regulating the solubility of the resin is being studied (see, for example, patent reference 2). However, this does not pose a radical solution to the problem, and fails to realize a fully satisfactory resolution of isolated line pattern.
Moreover, the microfabrication using a resist composition is not only directly used in the manufacturing of integrated circuits but also, in recent years, finds application in the fabrication of so-called imprint mold structures, etc. (see, for example, patent references 3, 4 and non-patent reference 1). In the fabrication of imprint mold structures as well, the influence of backward scattering becomes conspicuous in accordance with an increase of drawn area, thereby tending to invite a deterioration of resolution. Therefore, in the formation of an isolated pattern using, in particular, X-rays, soft X-rays or electron beams as an exposure light source as well, it is an important task to simultaneously satisfy high sensitivity, high resolution and favorable dry etching resistance, and is now needed to resolve this task.